This report presents the caise.messaging group communication framework, a simple Java-based Api developed as the networking component for a collaborative software engineering architecture. The framework is intended to be used as the communication layer for any distributed and/or collaborative systems that have communication requirements beyond simple point-to-point networking, but do not require the services or overheads of fully-featured groupware toolkits. The caise.messaging framework allows groups of remote applications to communicate with each other in the most simple manner as possible. The result is an Api that makes every participating application appear local to the calling application, providing communication within the application group by way of conventional method calls. This report presents an overview of the caise.messaging framework, including a background on existing communication technologies, the motivation for a new framework, a summary of the caise.messaging architecture, illustrated examples of caise.messaging-based tools, and Api details.